Influence of the blood bacterial load on the meningeal inflammatory response in Streptococcus pneumoniae meningitis

Background: Despite bacteraemia is present in the majority of patients with pneumococcal, little is known about the influence of the systemic infection on the meningeal inflammatory response. Methods: To explore the role of systemic infection on the meningeal inflammation, experimental meningitis was induced by intracisternal injection of similar to 1 x 10(6) CFU Streptococcus pneumoniae, type 3, and the 26 rabbits were either provided with similar to 1 x 10(6) CFU S. pneumoniae intravenously at 0 hour ("bacteraemic" rabbits, n = 9), immunized with paraformaldehyde-killed S. pneumoniae for 5 weeks prior to the experiment ("immunized" rabbits", n = 8), or not treated further ("control" rabbits, n = 9). WBC and bacterial concentrations were determined in CSF and blood every second hour during a 16 hours study period together with CSF IL-8 and protein levels. We also studied CSF and blood WBC levels in 153 pneumococcal meningitis patients with and without presence of bacteraemia. Results: As designed, blood bacterial concentrations were significantly different among three experimental groups during the 16 hours study period ( Kruskal Wallis test, P < 0.05), whereas no differences in CSF bacterial levels were observed ( P > 0.05). Blood WBC decreased in bacteraemic rabbits between similar to 10 - 16 hours after the bacterial inoculation in contrast to an increase for both the immunized rabbits and controls ( P < 0.05). The CSF pleocytosis was attenuated in bacteraemic rabbits as compared to the two other groups between 12 - 16 hours from time of infection ( P < 0.017), despite accelerated CSF IL-8 levels in bacteraemic rabbits. In patients with pneumococcal meningitis, no significant difference in CSF WBC was observed between patients with or without bacteraemia at admission ( n = 103, 1740 cells/mu L ( 123 - 4032) vs. n = 50, 1961 cells/mu L ( 673 - 5182), respectively, P = 0.18), but there was a significant correlation between CSF and blood WBC ( n = 127, Spearman rho = 0.234, P = 0.008). Conclusion: Our results suggest that a decrease in peripheral WBC induced by enhanced bacteraemia in pneumococcal meningitis results in an attenuated CSF pleocytosis.